Light - Reflection and Refraction

At focus F behind the mirror, highly diminished, point sized image is formed.

First law:
The incident ray, the normal to the surface at the point of incidence and the reflected ray, all lie in the same plane.

In convex mirrors or diverging mirrors, the reflecting surface is curved outwards.

The SI unit of power of a lens is "dioptre", which is denoted by 'D'.

Object distance (u), image distance (v) and focal length (f) of a spherical mirror are related as: 1/u + 1/v = 1/f

For spherical mirrors of small aperture, R = 2f.

Radius of curvature, R = 24 cm
Radius of curvature = 2 × focal length (f)
f = r/2
= 24/2
= 12 cm

The perpendicular distance between the direction of the incident ray and the emergent ray is called “lateral shift’’.

Power of a lens is defined as the reciprocal of its focal length. If P is the power of a lens of focal length f in metres, then p = 1/f.

A lens, either a convex lens or a concave lens, has two spherical surfaces.

Speed of light in glass = Speed of light in vacuum/refractive index of glass
= 3 × 10⁸/1.20
= 2.5 x 10⁸ m/s

Magnification produced by a spherical mirror is given by the relation,
m = h_i/h_o = - v/u
Height of the object, h_o = h

• 3h/h = - v/u
  Object distance, u = - 20 cm
  v = - 60 cm

The power of the given lens
= 1/f
= 1/- 4
= - 0.25 D

By using formula of deviation, we get  
(360 - 2q)
= (360 – 40 x 2)
= 280^o

Focal length of the convex mirror, f = + 10 cm
Object distance, u = - 5 cm
According to the lens formula, we get
1/v + 1/u = 1/f
1/v = 1/f - 1/u
= 1/10 - 1/- 5
v = 3 cm